It has been known in the art for some time to coat textiles, such as woven or knitted fabrics or non-woven bonded webs, with solutions or dispersions of polyurethanes by the direct or reversal process. The articles obtained are used for the manufacture of outerwear garments, upholstery, bags, suitcases, shoe upper material, tarpaulins, awnings and many other products.
In contrast to two-component polyurethanes, which have been known quite a long time, the so-called "one-component polyurethanes" have been more recently introduced into the art. These products are obtained by reacting mixtures of polyhydroxyl compounds, in practice mainly dihydroxypolyesters or dihydroxypolyethers, and glycols, preferably ethylene glycol or butane-1,4-diol, with aromatic diisocyanates, preferably diphenylmethane-4,4'-diisocyanates. These polyurethanes, which are substantially linear and can be prepared both in solution and in solvent-free melts, can be dissolved only in solvent mixtures which contain dimethylformamide or other highly polar compounds, such as dimethylacetamide or N-methyl-pyrrolidone, in proportions of from 20 to 60%, based on the total quantity of solvent. Solutions of the one-component polyurethanes have a practically unlimited pot-life.
The process of film formation of these one-component polyurethanes have a practically unlimited pot-life.
The process film formation of these one-component polyurethanes is a purely physical process which, in contrast to that of two component polyurethanes, is not accompanied by any chemical reaction.
Not only the use of glycols, such as butane diol, as chain lengthening agents for the preparation of one-component polyurethanes, but also the use of diolurethanes, diolamides and diolureas for the formation of the hard segments in polyurethanes is already known in the art (DOS No. 1,544,864).
Furthermore, segmented polyurethane elastomers are prepared from aromatic isocyanate prepolymers and aromatic or aliphatic diamines, bis-hydrazides, bis-semicarbizides, bis-carbazic acid esters and hydrazine hydrate as chain lengthening agents. In addition to the so-called "aromatic one-component polyurethanes", which are prepared from aromatic diisocyanates, the so-called "aliphatic one-component polyurethanes" are also already known in the art. These are polyurethane ureas obtained from higher molecular weight dihydroxy compounds, aliphatic diisocyanates and aliphatic diamines as chain lengthening agents.
One-component polyurethanes obtained from dihydroxypolyesters and/or dihydroxypolyethers, aromatic diisocyanates, diols and/or aromatic diamines and/or bis-hydrazides are used for the preparation of top coats and bonding coats by the reversal process in the form of from 20 to 40% solutions in solvent mixtures which always contain high proportions of dimethylformamide. One-component polyurethanes based on aliphatic diisocyanates and aliphatic diamines are applied from solvent mixtures which contain secondary or primary alcohols in addition to aromatic hydrocarbons.
The aromatic and aliphatic one-component polyurethanes are distinguished, among other things, by their high mechanical strength, high elongation, low abrasion loss and high folding strength. They are also characterised by the relatively high microhardness of films produced from the polyurethane solutions or dispersions (Shore A hardness 60-95) and the relatively high modulus values (100% modulus values are generally from 25 to 150 kp/cm.sup.2).
Textile coatings produced using such polyurethanes as bonding coat do not have the extremely soft napa-like hand which can be obtained by using the bonding pastes according to the invention.